Devices for identifying targets and directing a missile toward those targets are well-known. Basically, the conventional devices of this type fall into two categories:
1. Devices in which the missile itself detects, and zeroes in on, a source of energy such as heat or magnetic disturbance, and PA0 2. devices in which the missile is guided by remote control to a target in accordance with target information detected by an independent target-identifying apparatus.
In the latter type of device, the target area is generally evaluated by a scanning system mounted on an aircraft or the like. The system observes the target area, calculates the apparent displacement of stationary objects in the field of view between successive scans, compares successive displacement-compensated scans, and by a subtraction process identifies targets which fail to conform to the predicted pattern of apparent movement of stationary objects. Because of the nature of the motion of an aircraft, the size of the target area seen by the scanner remains essentially constant throughout the target acquisition interval, so that the only correction which needs to be made is the correction for linear position changes along the path of the aircraft.
A totally different situation arises if the detection device is to be mounted directly within a projectile or small missile in which cost and space factors are predominant. Due to the nature of the trajectory of the projectile in travelling toward a target, the image of the target area as seen by a detector on the projectile appears to expand radially outward from a central point. The use of conventional computational methods in compensating for this type of motion requires apparatus too bulky and expensive for use in a projectile. For this reason, it has heretofore been impractical to mount self-contained moving target detectors directly within a projectile. This is particularly true for infrared detectors which inherently have low resolution and require a substantial number of frames to detect target movement.